I have the problem since today that I cannot embed / upload any images or files anymore in my Confluence page. Neither copy-pasting of pictures work, nor when I type /image nor when I try to use the macro using the "+":

Nothing happens when I click on "Image, video, or file". The popup window doesn't open, but I also don't get any error messages.
I tried different spaces, even with my own personal space where I have full permissions to do anything I want. It still worked flawlessly yesterday and suddenly today it stopped worked. I tried with different browsers Chrome and Edge, but no difference.
Interestingly if I try completely different Confluence instance (sort of my personal Confluence sandbox) there it still works. I can upload / embed pictures normally.
Is this some kind of strange configuration / security setting that suddenly got activated? Or was there some Confluence release update running in the background which is causing this unwanted effect?